Doherty amplifiers are used conventionally to construct high-frequency amplifiers with high efficiency and high linearity.
From European Patent EP 1 609 239 B1, a Doherty amplifier is known which uses a 3 dB coupler simultaneously as impedance transformer for the main amplifier and as power combiner for the main and auxiliary amplifier by terminating the decoupled terminal of the 3 dB coupler, normally terminated with the system wave impedance, with a short-circuit or open-circuit line of given length. The arrangement shown in that context has the disadvantage that a frequency change beyond the conventional Doherty bandwidth is not possible, and the space requirement for a low-loss line is relatively large.
What is needed, therefore, is a high-frequency amplifier which, with a high efficiency and high linearity, demands a small space requirement and simultaneously allows a high flexibility in circuit construction.